Helmet Size Calculator
Find your motorcycle, bicycle or ski helmet size (XS to 3XL) from your head circumference in cm or inches, with the full size chart and tips for when you are between sizes.
How it works
Size = the chart row where lower bound ≤ head circumference < upper bound · inches × 2.54 = cm · motorcycle sizes step every 2 cm (M = 57–58 cm), bicycle and ski sizes cover 3–4 cm each
Helmets are sized by head circumference measured just above the eyebrows and ears, around the fullest part of the back of the head. Motorcycle helmets use narrow 2 cm steps because the padding must fit snugly to keep the helmet in place in a crash; bicycle and ski helmets have an adjustable retention dial, so each size spans 3–4 cm. The chart reflects the most common industry sizing, but brands differ by a centimetre or so and head shape (round or long oval) matters — always check the maker’s chart and try the helmet on.
Worked example
A 57 cm head (22.44″) falls in the motorcycle range 57–59 cm, so it fits a size M helmet, at the bottom of the range — it is also worth trying an S. The same head is a size M in bicycle helmets (55–59 cm).
Sources: NHTSA — Choose the right motorcycle helmet · CPSC — Which helmet for which activity
Frequently asked questions
How do I measure my head for a helmet?
Wrap a soft tape measure around your head about 2.5 cm (1 inch) above your eyebrows and just above your ears, around the widest part at the back. Take the largest of three measurements.
What size helmet is 58 cm?
Usually a medium: 57–59 cm in most motorcycle charts and 55–59 cm for bicycles. If it feels loose, try a small shell with thicker pads.
Should a helmet be tight?
A motorcycle helmet should be snug all round with even pressure and no hot spots; when you move it, your skin should move with it. Bicycle helmets should not rock more than about 2.5 cm in any direction once the dial is tightened.
What if I am between two sizes?
Try both. For motorcycle helmets most riders choose the smaller one, since the comfort liner compresses by up to 1 cm with use. For bike and ski helmets the larger size with the dial tightened is usually fine.
Are helmet sizes the same for every brand?
No. Most brands follow similar centimetre ranges, but shells and padding differ, and some brands use intermediate-oval versus round-oval head shapes. Use this as a starting point.
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This calculator is for educational purposes. Double-check important results before acting on them.